Linear Compressor Cylinder and Head Construction

ABSTRACT

A cylinder and head assembly for a linear compressor has a cylinder chassis ( 35, 11 ), a cylinder liner ( 12 ) open at both ends and a valve plate ( 5 ) defining a barrier between the compression end ( 37 ) of the cylinder liner ( 12 ) and the head space ( 7 ) defined by the cylinder chassis. The valve ( 5 ) plate is located between an annular shoulder ( 39 ) of the cylinder chassis ( 35 ) and an open end of the cylinder liner ( 37 ).

FIELD OF THE INVENTION

The present invention relates to linear compressors, and in particular linear compressors of the type suitable for use in a vapour compression refrigeration system.

BACKGROUND TO THE INVENTION

Linear compressors of a type for use in a vapour compression refrigeration system are the subject of many documents in the prior art. One such document is our co-pending PCT patent application PCT/NZ2004/000108. That specification describes a variety of developments relating to compressors, many of which have particular application to linear compressors. The present invention relates to further improvements to compressor embodiments such as those described in that patent application. Accordingly that application provides a general exemplification of a compressor to which the present invention may be applied. However the present invention may also be applied beyond the scope of the particular embodiments of a linear compressor disclosed in that application. Persons skilled in the art will appreciate the general application of the ideas herein to other embodiments of linear compressors such as are found in the prior art.

The present invention relates generally to cylinder part and head assemblies.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a cylinder and cylinder head assembly with improved characteristics with particular application to linear compressors, or to at least provide the industry with a useful choice.

In a first aspect the invention may broadly be said to consist in a cylinder and cylinder head assembly for a linear compressor comprising:

a cylinder chassis including an inner surface defining a cylinder head space at one end and a cylinder space extending along an axis from said cylinder head space, said cylinder space being at least substantially cylindrical, with an outlet from said cylinder head space through the wall of said cylinder chassis,

a cylindrical cylinder liner, open at both ends and located within said frame, such that the outer surface of said liner is engaged against the cylinder space defining portion of said inner surface of said chassis, and

a valve plate defining a barrier between a compression end of said cylinder liner and said head space, said valve plate engaged between said cylinder chassis and said cylinder liner to locate said valve plate against the open end of said cylinder liner.

According to a further aspect of the invention said cylinder chassis extends beyond the other end of said cylinder liner, and may carry, for example, stator parts of a linear motor. Alternatively said cylinder chassis may end intermediate the ends of said cylinder liner, to cover only a portion of the outer surface of the cylinder liner. In that case a separate cylinder part frame may be fixed over the other end of the cylinder liner, for example with an interference friction fit. The cylinder part frame may carry the stator parts of a linear motor.

According to a further aspect of the invention the valve plate is not fixed to the cylinder liner, but alternatively it may be, for example by solder or brazing, or by adhesive.

According to a further aspect of the invention said cylinder liner is an interference fit within said chassis and is held in place by friction.

According to a further aspect of the invention said chassis includes, at a transition between said cylinder defining part of said inner surface and said head defining part of said inner surface, a shoulder or shoulders, and said valve plate is pressed between said shoulder or shoulders at one side and the annular end of said cylinder liner at its other side.

The shoulder may be annular or may be an annular series of inwardly protruding shoulders. The shoulder may press directly against the face of the valve plate, or may press against the face of a valve plate via an intermediate component, such as a resilient spring or gasket. A gasket may be interposed between the annular end of the cylinder liner and the valve plate.

The valve plate may include one or more valve members assembled to it.

One or more grooves in either the inner surface of the cylinder chassis or the outer surface of the cylinder liner may define supply passages to supply compressed gases to gas bearing ports formed in the cylinder liner. Preferably these grooves are provided in the outer surface of the cylinder liner, for example as described in our PCT Application WO 02/35093. In that case one or more notches are preferably provided in the periphery of the valve plate to define a flow path between the compressed gases discharge space and the head and the gas bearing supply passages defined between the chassis and the liner.

In a further aspect the present invention may broadly be said to consist in a refrigeration system compressor comprising a hermetic housing, a linear compressor within said hermetic housing, said compressor including a cylinder part assembly at least in part defined according to one or more of the above paragraphs, a piston part including a piston for reciprocating within the cylinder defined by said cylinder liner, and a linear electric motor for driving reciprocating movement between the piston part and cylinder part, with the linear compressor suspended for operation within said hermetic housing.

In a still further aspect the present invention may broadly be said to consist in a method of manufacturing a linear compressor, including, for assembling the cylinder and head portion thereof, the steps of:

by differential temperature, expanding a cylinder chassis relative to a cylinder liner part,

inserting a valve plate defining barrier into said cylinder chassis through an open end thereof,

inserting said cylinder liner part into said cylinder chassis through said open end to engage said valve plate between an end of said cylinder liner and said cylinder chassis to define a barrier between a compression end of said cylinder and a head space enclosed by said cylinder chassis, and

retaining a said cylinder liner in this position until said cylinder chassis and said cylinder liner become engaged as said temperature differential reduces.

To those skilled in the art to which the invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the scope of the invention as defined in the appended claims. The disclosures and the descriptions herein are purely illustrative and are not intended to be in any sense limiting.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevation in cross-section of a linear compressor with a cylinder part assembly incorporating the invention according to one preferred embodiment.

FIG. 2 is an external perspective of the cylinder head end portion of the cylinder part according to one preferred embodiment of the present invention.

FIG. 3 is a cross-section side elevation of the cylinder part portion of FIG. 2 according to one embodiment of the present invention.

FIG. 4 is a cross-section side elevation of the cylinder part portion of FIG. 2 according to another embodiment of the present invention.

DETAILED DESCRIPTION

Referring to FIG. 1 the compressor for a vapour compression refrigeration system includes a linear compressor I supported inside a housing 2. Typically the housing 2 is hermetically sealed and includes a gases inlet port 3 and a compressed gases outlet port 4. Uncompressed gases flow within the interior of the housing, surrounding the compressor 1. These uncompressed gases are drawn into the compressor during intake stroke, compressed between the piston crown 14 and outlet valve plate 5 on the compression stroke and expelled through discharge valve 6 into a compressed gases manifold 7. Compressed gases exit the manifold 7 to the outlet port 4 in the shell through a flexible tube 8. To reduce the stiffness effect of discharge tube 8 the tube is preferably arranged as a loop or spiral transverse to the reciprocating axis of the compressor.

The intake to the compression space may be through the piston (with an aperture and valve in the crown) or through the head, divided to include suction and discharge manifolds and valves.

The illustrated linear compressor 1 has, broadly speaking, a cylinder part and a piston part connected by a main spring. The cylinder part includes cylinder chassis 10, cylinder head 11, valve plate 5 and a cylinder liner 12. The cylinder part also includes stator parts 15 for a linear electric motor. An end portion 18 of the cylinder part, distal from the head 11, mounts the main spring relative to the cylinder part. In the illustrated embodiment the main spring is formed as a combination of coil spring 19 and flat spring 20.

The piston part includes a hollow piston 22 with sidewall 24 and crown 14. A rod 26 connects between the crown 14 and a supporting body 30 for linear motor armature 17. The rod has a flexible portion 28 in approximately the centre of the hollow piston 22. The linear motor armature 17 comprises a body of permanent magnet material (such as ferrite or neodymium) magnetised to provide one or more poles directed transverse to the axis of reciprocation of the piston within the cylinder liner. An end portion 32 of armature support 30 which is distal from the piston 22 is connected with the main springs 19, 20.

The linear compressor 1 is mounted within the shell 2 on a plurality of suspension springs to isolate it from the shell. In use the large outer body of the linear compressor, the cylinder part, will oscillate along the axis of reciprocation of the piston part within the cylinder part. In the preferred compressor the piston part is purposely kept very light compared to the cylinder part so that the oscillation of the cylinder part is small compared with the relative reciprocation between the piston part and cylinder part. In the illustrated form the linear compressor is mounted on a set of four suspension springs 31 generally positioned around the periphery. Alternate suspension spring arrangements are illustrated in PCT/NZ2004/000108. The ends of each suspension spring fit over elastomeric snubbers connected with the linear compressor 1 at one end of each spring and connected with the compressor shell 2 at the other end of each spring.

This briefly describes a linear compressor of a type for which the improved head assembly of the present invention is useful. However it will be appreciated that the usefulness of the present invention is not restricted to linear compressors of the type and configuration illustrated. The improvement is generally applicable.

The present invention provides a manner of manufacture of the cylinder and cylinder head portion of the linear compressor which reduces the parts involved and improves the reliability of the connections, thereby improving manufacture, cost and compressor reliability. The relevant portion of the linear compressor illustrated in FIG. 1 is further illustrated in FIGS. 2 and 3. A slight variation is illustrated in FIG. 4. in this manner of manufacture the head cover is incorporated in the main chassis component of the cylinder part 10. Preferably it is incorporated as an integral part, for example cast integrally with the remainder of the frame when the frame is manufactured. Thus the head 11 appears as a cap enclosing one end of cylinder body 35.

A valve plate is secured in position within the cylinder chassis to divide a head portion of the space therein from a cylinder portion of the space therein. The valve plate includes at least a discharge valve aperture, and preferably carries a discharge valve fixed on one side.

The inner surface of the cylinder portion 35 of the chassis is preferably cylindrical and the outer perimeter of the valve plate is preferably circular and sized to fit closely within the cylindrical surface.

The cylinder liner 12 has a cylindrical outer surface sized to have an interference fit within the inner surface of cylinder portion 35. This provides that when the cylinder liner 12 and the cylindrical portion 35 of the cylinder chassis are at the same or similar temperature, and the cylinder liner 12 is in place within the cylinder chassis, the two parts are tightly engaged without requirement for further fixing or fastening.

The periphery of valve plate 5 is engaged between the end 37 of cylinder liner 12 and the cylinder chassis. Preferably the cylinder chassis includes an annular shoulder 39 and the shoulder 39 and end 37 of the cylinder liner directly engage opposite sides of the periphery 38 of the valve plate. Alternatively a plurality of shoulder portions may be provided distributed around the periphery of the valve plate, or an intermediate spacer may be provided between either the cylinder chassis and the valve plate 5 or between the cylinder liner 12 and the valve plate 5.

The valve plate 5 may be provided with an annular rebate 40 at periphery 38 to receive the end of cylinder liner 12.

An embodiment including an intermediate spacer is depicted in FIG. 4. In this embodiment the spacer is not a simple cylindrical ring or similar. Instead the spacer is an annular spring 42. The spring 42 and valve plate 5 are both engaged between the cylinder chassis and the cylinder liner. The annular spring 42 butts against shoulder 39 and against the periphery 38 of valve plate 5.

A gasket 43 may be included in the assembly, for example as illustrated in FIG. 4, sandwiched between the periphery 38 of the valve plate 5 and the end 37 of cylinder liner 12. The gasket may be provided in a recess 40 around the periphery of the valve plate.

The preferred method of assembly of this part of the compressor involves heating the cylinder chassis (which is typically cast aluminium alloy) and then placing the valve plate within the cylindrical cavity to butt against the shoulder 39. In the case of the embodiment of FIG. 4 the spring spacer is inserted first. The cylinder liner 12 is then pushed firmly into the cylindrical cavity against the valve plate and is retained there until the cylinder shrinks onto it. With reasonable manufacturing tolerances it should be possible to achieve this consistently and with very effective eventual engagement between the cylinder liner 12 and the cylinder chassis by heating the cylinder chassis to approximately 250° C. and leaving the liner at room temperature.

This manner of manufacture can eliminate a number of parts, the head cover and whatever bolts or fasteners would otherwise be used to secure it, and can eliminate the potential for a leak path through any gasket between the head and the end of the cylinder. In the compressor of the present invention the only leak path from the head can be back around the valve plate into the compression space in the cylinder.

The cylinder part assembly of the present invention is preferably applied where there is only a discharge valve in the head assembly, with the suction valve for the compressor being included in the crown of the piston and the gases intake occurring through the body of the piston. However the manner of manufacture can also be used where suction and discharge occur through the cylinder head, but particular care would need to be taken to ensure an adequate seal at any division between the suction side and discharge side within the head enclosure.

The embodiment of FIG. 4, where a spring is provided interposed between the valve plate and the cylinder chassis, ensures an effective clamping pressure over a wider tolerance of insertion location of the liner 12 within the cylinder frame. This arrangement has the added advantage that the valve plate can lift slightly if the piston collides with the valve plate in operation. This may reduce noise from the collision and any damage to the piston face and linkages between the piston and linear motor armature.

The arrangement of the present invention contrasts with the usual arrangement where the head or cover is a separate component that is bolted or otherwise secured to the cylinder part frame, generally with the edge of the valve plate sandwiched between the end of the cylinder part frame and the end of the head or cover. 

1. A cylinder and cylinder head assembly for a linear compressor comprising: a cylinder chassis including an inner surface defining a cylinder head space at one end and a cylinder space extending along an axis from said cylinder head space, said cylinder space being at least substantially cylindrical, with an outlet from said cylinder head space through the wall of said cylinder chassis; a cylindrical cylinder liner, open at both ends and located within said frame, such that the outer surface of said liner is engaged against the cylinder space defining portion of said inner surface of said chassis; and a valve plate defining a barrier between a compression end of said cylinder liner and said head space, said valve plate engaged between said cylinder chassis and said cylinder liner to locate said valve plate against the open end of said cylinder liner.
 2. A cylinder and cylinder head assembly as claimed in claim 1, wherein said cylinder chassis extends beyond the other end of said cylinder liner.
 3. A cylinder and cylinder head assembly as claimed claim 1, wherein said cylinder chassis ends intermediate the ends of said cylinder liner, to cover only a portion of the outer surface of the cylinder liner.
 4. A cylinder and cylinder head assembly as claimed in claim 3, wherein a separate cylinder part frame is fixed over the other end of the cylinder liner.
 5. A cylinder and cylinder head assembly as claimed in claim 4, wherein said cylinder part frame is fixed over the other end of the cylinder liner with an interference friction fit.
 6. A cylinder and cylinder head assembly as claimed claim 4, wherein the cylinder part frame carries the stator parts of a linear motor.
 7. A cylinder and cylinder head assembly as claimed in claim 1, wherein the valve plate is not fixed to the cylinder liner.
 8. A cylinder and cylinder head assembly as claimed in claim 1, wherein said cylinder liner is an interference fit within said chassis and is held in place by friction.
 9. A cylinder and cylinder head assembly as claimed in claim 1, wherein said chassis includes, at a transition between said cylinder defining part of said inner surface and said head defining part of said inner surface, a shoulder or shoulders, and said valve plate is pressed, on opposite sides, between said shoulder or shoulders and the annular end of said cylinder liner.
 10. A cylinder and cylinder head assembly as claimed in claim 9, wherein the shoulder is annular.
 11. A cylinder and cylinder head assembly as claimed in claim 9, wherein the shoulder is an annular series of inwardly protruding shoulders.
 12. A cylinder and cylinder head assembly as claimed in claim 9, wherein the shoulder presses directly against the face of the valve plate.
 13. A cylinder and cylinder head assembly as claimed in claim 9, wherein the shoulder presses against the face of a valve plate via an intermediate component.
 14. A cylinder and cylinder head assembly as claimed in claim 13, wherein the intermediate component is a gasket or resilient spring.
 15. A cylinder and cylinder head assembly as claimed in claim 13, wherein a gasket is interposed between the annular end of the cylinder liner and the valve plate.
 16. A cylinder and cylinder head assembly as claimed in claim 1, wherein the valve plate includes one or more valve members assembled to it.
 17. A cylinder and cylinder head assembly as claimed in claim 1, wherein one or more grooves in either the inner surface of the cylinder chassis or the outer surface of the cylinder liner define supply passages to supply compressed gases to gas bearing ports formed in the cylinder liner.
 18. A cylinder and cylinder head assembly as claimed in claim 17, wherein these grooves are provided in the outer surface of the cylinder liner.
 19. A cylinder and cylinder head assembly as claimed in claim 17, wherein one or more notches are provided in the periphery of the valve plate to define a flow path between the compressed gases discharge space and the head and the gas bearing supply passages defined between the chassis and the liner.
 20. A linear compressor comprising a refrigeration system compressor comprising a hermetic housing, a linear compressor within said hermetic housing, said compressor including a cylinder part assembly as claimed in claim 1, a piston part including a piston for reciprocating within the cylinder defined by said cylinder liner; and a linear electric motor for driving reciprocating movement between the piston part and cylinder part, with the linear compressor suspended for operation within said hermetic housing.
 21. A method of manufacturing a linear compressor, including, for assembling the cylinder and head portion thereof, the steps of: by differential temperature, expanding a cylinder chassis relative to a cylinder liner part, inserting a valve plate defining barrier into said cylinder chassis through an open end thereof, inserting said cylinder liner part into said cylinder chassis through said open end to engage said valve plate between an end of said cylinder liner and said cylinder chassis to define a barrier between a compression end of said cylinder and a head space enclosed by said cylinder chassis, and retaining a said cylinder liner in this position until said cylinder chassis and said cylinder liner become engaged as said temperature differential reduces.
 22. (canceled) 